Approximately one-half million bicycles are stolen each year, and many are stolen because they are inadequately locked. Bicycling magazine (August, 1994) reports test results in which most portable bicycle locks were violated in less than one minute. To combat theft, two general systems of portable bicycle locks have been developed in prior art. Each kind of lock has a different weakness, which may allow the bicycle to be stolen with relative ease.
A first kind of lock includes one or more elements such as a lock, shackle, or cable) that is external to or carried by the bicycle frame. This kind of lock attempts to secure the bicycle to a stationary external object. Because these locks have at least one component that is external to the bicycle frame, the locks can be broken using simple hand tools, such as bolt cutters to cut a cable, an automobile jack to pry a lock open,or a hammer to shatter a lock that a thief made brittle by subjecting it to extreme cooling with dry ice or liquid nitrogen. With this class of devices, the external components of the lock can be broken or compromised without damaging the bicycle or disturbing its operation. The stolen bike is usable and sellable.
A second kind of bicycle lock eliminates the weakness of an external element by keeping the locking system essentially entirely within the bicycle frame. This kind of lock makes the bicycle non-functional, but the bicycle can nevertheless be stolen merely by picking it up and carrying it to another location where the internal lock can be broken or removed using more sophisticated tools. An example of this is U.S. Pat. No. 3,774,421 (Stephens) where the horizontal top tube of a bicycle frame includes a lock and a chain is stored within the top tube. In use, however, the chain in the locking mode can be easily cut by a thief.
To effectively prevent theft, a locking system must have two characteristics: (a) every piece of the locking system must be protected within the bicycle, so that breaking the lock causes damage to the bicycle, and (b) the lock must secure the bicycle to a fixed external object. In order to meet these geometric requirements, the bicycle frame itself should function as a lock.
The art of folding bicycles broadly suggests the use of articulating bicycle frame parts so as to make the bicycle smaller and more easily transported or stored. U.S. Pat. No. 4,417,745 (Shomo) discloses a bicycle which hinges inter alia about a vertical hinge located in the bicycle frame. This bicycle along with most or all other folding bicycles, serves no anti-theft purpose. Folding bicycles with their myriad of folding parts requires manufacturing considerably different from a standard bicycle. Components to separate a bicycle for packing in a wheel-sized carrying case have been sold by S and S Machine, Roseville, Calif. Torque couplings are provided to separate one end of the bicycle top tube, one end of the down tube and the front fork from the seat tube, the pedal crank housing and the rear fork. Italian Patent No. 360,530 (Ascaralli) shows separation of a head tube from a top tube, seat tube and a bottom tube leading to the pedal crank housing. French Patent No. 883,836 also shows a folding bicycle having a series of pivoting joints in each of the bicycle frame tubes with one end of a top tube being demountable from the seat tube. None of the above collapsible or folding bicycles serve any anti-theft purpose. U.S. Pat. No. 3,814,462 (Kelly) shows an anti-theft bicycle frame where one end of a top tube is split and lockable to a stub end of the top tube attached to the seat tube and where the forwardly extending diagonal frame members i.e. most of the fixed top tube, the head tube and the down tube are pivotably connected to the pedal crank housing. This necessitates the whole bicycle or at least a pivoted half to be lifted to open the bicycle as seen in FIG. 5 of Kelley and the need for a special pivoting joint at the crank housing or otherwise, where the bicycle is lifted off the ground in order to open the frame.
From the above it is seen that there has been a need for a simple but effective locking system contained in the structure of the bicycle 1) where damaging the lock or top tube damages and immobilizes the bicycle, 2) where the bike can be simply and easily leaned against a pole or tree or other immovable structural member, so that the bicycle can be relocked and then cannot be carried away by a thief and 3) where these needs can be accomplish with a standard bicycle frame slightly modified and enabling manufacture using standard processes.